地层衰减对地震波速度逆散射反演的影响研究

在利用地震波数据进行地球物理反演时,地层对地震波的吸收衰减效应会对地层物性参数的准确反演产生较大的影响,因此利用黏弹性声波方程进行反演更符合实际情形.本文在考虑地层衰减效应进行频率空间域正演模拟的基础上,提出基于黏弹性声波方程的频率域逆散射反演算法并对地震波传播速度进行反演重建,在反演过程中分别用地震波传播复速度和实速度来表征是否考虑地层吸收衰减效应.基于反演参数总变差的正则化处理使反演更加稳定,在反演中将低频反演速度模型作为高频反演的背景模型进行逐频反演,由于单频反演过程中背景模型保持不变,故该方法不需要在每次迭代中重新构造正演算子,具有较高的反演效率;此外本文在反演过程中采用了基于MPI的并行计算策略,进一步提高了反演计算的效率.在二维算例中分别对是否考虑地层吸收衰减效应进行了地震波速度反演,反演结果表明考虑衰减效应可以得到与真实模型更加接近的速度分布结果,相反则无法得到正确的地震波速度重建结果.本文算法对复杂地质模型中浅层可以反演得到分辨率较高的速度模型,为其他地震数据处理提供比较准确的速度信息,在地层深部由于地震波能量衰减导致反演分辨率不太理想.

Effect of stratigraphic attenuation on inverse-scattering seismic velocity inversion

The attenuation effect can influence the precision of inversion of Earth's physical properties when solving geophysical inverse problems utilizing seismic data. Therefore using the viscoelastic acoustic wave equation is more suitable for the actual situation. In this paper, based on seismic forward modeling considering the attenuation effect in the frequency-space domain, the inversion algorithm with inverse scattering based on viscoelastic acoustic equation is applied in the frequency domain to reconstruct seismic velocity distribution. Real or complex velocity is used individually in the inversion process depending on whether the earth attenuation effect is considered. Meanwhile the regularization of inversion parameter's total variation makes this inversion approach more stable. Frequency-divided inversion strategy is adopted, the lower frequency inversion result is set as the background model of higher frequency inversion, and the background model remains constant during the inversion process for a particular frequency. So this inversion method does not need to reconstruct the forward operator in each iteration, which makes it more efficient. In order to improve the efficiency of inversion calculation further, the MPI parallel computing strategy is used in the procedure of inversion. In a 2D numerical example, the inversion algorithm is applied with and without considering the attenuation effect respectively. The results from the former approach is closer to the real velocity model, while the latter cannot match the real model. This algorithm can achieve high-resolution velocity reconstruction results for complex geological models at shallow and middle layers, and can provide accurate velocity information for other seismic data processing. While the inversion resolution is not ideal for a deep layer due to the attenuation of seismic energy.